MIniaturized-Cell-Enhanced PhotoAcoustic Spectroscopy

The laser spectroscopy techniques provide high-sensitivity and authentic detection of substances. They are reliable tools for real-time analyzing of trace amounts of chemical compounds in gas media. Sometimes, laser spectroscopy specialists say that they capable to identify the fingerprints of chemicals.

We are a research group specialized in development of laser-spectroscopy techniques and adaptation of them to needs of practical applications. We work in Laboratory of Optical Diagnostics at B.I.Stepanov Institute of Physics (NASB). Our current activity is associated with the photoacoustic technique of gas detection. The principle of the technique is based on measuring the amplitude and phase for the acoustic pressure oscillation (the so-called photoacoustic response) arising due to absorption of a modulated laser beam by molecules inside a photoacoustic cell-resonator. On the theory, the high-sensitivity photoacoustic detection of gases can be performed when the photoacoustic cell-resonator is essentially miniaturized. We try to implement the theory expectations in practice. Possible advantages/disadvantages associated with the miniaturization of photoacoustic hardware are under our investigation in the framework of ISTC B-1252 project).

To the moment, our efforts are concentrated on the miniaturized resonant photoacoustic cells . The design of such cells is optimized so as to obtain the best performance at an acoustic resonance of the cell (See on the optimization here).The optimization implies also an essential size reduction for the cells.

The photos demonstrate our achievements in the field.

Here is our recent miniaturized photoacoustic cell. The volume of internal cavity for the cell is ~ 5 mm3. We have an experience how to design, manufacture, test and apply such cells.Despite the reduced sizes, the developed cells are comparable in the performance (that is, in the sensitivity) with respect to non-miniaturized ones. The minimal detectable absorption estimated from our experiment for the cells is down to ~ 10-9 cm-1 W Hz-1/2. Such a millimeter-sized cell powered by the minute commercially available laser source (for instance, a near-infrared distributed-feed-back laser diode or mid-infrared quantum cascade laser) with a typical output power of ~ 10 mW will allow to detect trace gases at a sensitivity level, which can be attained by the absorption spectroscopy techniques along the optical path longer than 100 km.

The device shown at the right side of the photo is a recently developed hand-held version of MICEPAS gas sensor. The sensor is a combination of our photoacoustic cell with a commercially available near-infrared single-mode laser diode. In general, the sensor is intended for reliable on-line evaluation of the content of an individual volatile substance (any tracer gas, which is able to absorb the near-infrared light) in a gas mixture under conditions that the minimal detectable gas concentration can be smaller than 1 ppm. The shown MICEPAS sensor is designed to detect tracer-gas leaks emitted in air by a localized object at a leak rate down to ~ 5·10-8 mbar l/s. For comparison, the best gas-leak performance of standard portable halogen/hydrogen/helium sniffer leak detectors attains a rate value of ~ 10-6 mbar l/s.

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